Lighting may be provided by a great variety of different types of light sources. The light source is typically provided in the form of lighting modules comprising one or more light sources in a housing.
One example of a today well established light source is light emitting diodes (LEDs). LED modules typically comprise one or more LEDs arranged in a housing. The LEDs are typically provided on an LED chip, which may comprise further components. The housing has a light exit window through which the light emitted by the LEDs exits.
The light exit window may be made of a ceramic such as alumina. In order to provide a desired color of the provided light, the light exit window may be coated. Commonly used coatings include phosphor coatings, for providing a e.g. yellow colored light. As an example, one way to achieve white light is to combine an LED chip providing blue light with a phosphor coated light exit window, through which the blue LED light passes. As a result of the combination, a white colored output light is obtained.
It is desirable to achieve a lighting module providing light with predetermined characteristics, such as light color, light diffusion, color temperature, light intensity, color hue, and color value. There are many different approaches to improve the light characteristics. For example, for lighting modules comprising coatings, one problem is that variations in the coatings may have a high impact on the characteristics of the output light. Variations in characteristics such as thickness, uniformity and layer density leads to varying light characteristics. Thus, it may be difficult to control the manufacturing of the lighting module such that the desired light characteristics are obtained. Further, it may be difficult to obtain the same light characteristics for each lighting module in a batch of lighting modules.
Development of improved coatings and improving the control of the coating may alleviate this drawback. For example, U.S. Pat. No. 7,879,258 discloses a phosphor layer for an LED module which improves the light quality and provides for a method of tuning the light-diffusing properties by adjusting the phosphor layer.
This is one example of how a light characteristic may be improved. It is of course desirable to further improve the light characteristics and the control thereof for lighting modules such as LED modules.